This invention relates to naphthalimide compounds and their use in tissue bonding and protein cross-linking. This invention also pertains to devices and methods for arterial repair, preservation of expanded internal luminal diameters, and local delivery of drugs, skin care materials, sunscreens, and cosmetics.
Wound closure in body tissues while maintaining low levels of inflammation with resulting granuloma formation and attaining patency against leakage across the walls of luminal structures such as blood vessels remains a significant problem in surgical and trauma practice. Current closure practices involving sutures or mechanical devices such as clips, staples, or nails result in the introduction of foreign materials, which are sources of foreign body reactions and inflammation, and the formation of holes through luminal walls by the closing agent, which serve as potential avenues of post-operative fluid leakage and loss of luminal patency.
From catgut to synthetic polymers, sutures have been the traditional tool for vascular repair. However, fistulas and granulomas can form as a result of intolerance to the suture material. Suture techniques can also result in smaller residual lumens and reduced perfusion. These side effects can lead to necrosis, healing disorders, and ultimate dehiscence of the wound. Furthermore, leakage from the needle puncture sites can be problematic, particularly in cerebral applications or in patients with a compromised ability to achieve hemostasis (i.e. hemophiliacs or patients undergoing anticoagulant therapy). Finally, suture techniques are tedious and time-consuming, requiring a concerted effort on the part of the surgeon and therefore contributing to overall expense.
Mechanical assists such as staples and vascular clips have been proposed to facilitate tissue repair. While they do shorten operative times, the associated expense and potential risk of clip failure raise questions regarding their benefits over sutures. Furthermore, some staples require removal and may be associated with more patient discomfort.
Laser thermal tissue welding experiments report mixed results in achieving tissue bonds. Numerous infrared wavelengths, including those of the Nd:YAG, Argon, and CO2 lasers, have been tried. Laser welding has proven to be an exacting methodology, where insufficient exposures result in ineffective tissue bonding and high temperatures are associated with tissue destruction. In fact, the requisite denaturation of proteins (with tissue temperatures in the range of 60-80° C.) and associated collateral thermal damage appear to be the primary limiting factors for this technique.
Inflammation arising from foreign-material based wound closing agents can result, for example, in sufficient scarring to seriously impede function such as by imposing a barrier to laminar blood flow in a blood vessel possibly leading to clot formation and subsequent complications, or by degrading the desired cosmetic effects in skin plastic or trauma repair surgery.
Tissue adhesives comprising protein species, synthetic polymers, and biological materials have been advocated for wound repair to eliminate or minimize mechanical or foreign body effects. Protein based systems such as fibrin solutions and sprays offer hemostasis but little in the way of mechanical strength in holding opposing surfaces together. Synthetic polymeric glues such as polylactates and polyglycolates offer mechanical strength, but their products of chemical attachment in tissue are toxic and inflammatory. Acrylic based cements offer strength but are confined to external use on skin wounds because they are toxic and as a film impede migration of molecular and cellular species across bonded surfaces. Tissue adhesives incorporating aldehyde based protein cross-linking agents such as BioGlue™ have been used. However, long term diffusion of the aldehyde species away from the binding site leads to deleterious inflammation and granuloma formation.
The concept of a “patch” is also known. Various vascular repair procedures, notably carotid endarterectomy closure, have utilized numerous patch materials. It is important to note that this type of patching requires tailored fitting and extensive suturing to repair the site of injury. However, there are some associated benefits. The use of a patch helps avoid residual stenosis and decreases the likelihood of restenosis. Furthermore, a patch makes for easier closure under these difficult conditions and suffers less perioperative thrombosis. The size and shape of the patch are important to long-term success. A patch that is too large can lead to increases in wall stress and ultimate dilation or rupture. Large deviations from the native lumen size can also lead to increases in turbulence in blood flow, often associated with low shear rates and progression of the atherosclerotic process in arteries that are so predisposed. Experience would suggest that a long, tapered, panhandle shaped patch serves better than an oval patch to maximize the benefits and avoid potential risks.
What is needed is a method of applying a patch over an arterial lesion which achieves structural competency and hemostasis without attendant leakage of blood through the luminal wall and patch, granulomatous tissue growth into the vessel lumen, decrease in luminal area due to foreign body reaction, and initiation of intraluminal clot formation.
Prior tissue bonding technology using 4-amino-1,8-naphthalimide biomolecular cross-linking has successfully achieved tissue closure without inflammatory reactions or penetration by foreign objects. (U.S. Pat. Nos. 5,235,045; 5,565,551; 5,766,600; 5,917,045; and 6,410,505; the content of each of these patents is incorporated by reference herein). This tissue bonding technology requires the application of light having a wavelength within the absorption spectrum of 400-500 nm (blue light) to the photochemical upon the tissue or biomaterial surfaces in order to initiate the photochemical bonding process. Minimization of light requirements would facilitate the ease of use for clinicians.
What is also needed, therefore, is a means of attaching two tissue surfaces together or a tissue surface to a compatible biomaterial to effect wound closure that does not introduce a material that induces an inflammatory reaction or compromise the structural integrity of a luminal wall. What is further needed is a means of attaching two tissue surfaces or a tissue surface and a compatible biomaterial that does not require direct application of light to the tissue surfaces being attached.
Concerns also exist for the long-term retention of the opened arterial lumen after balloon dilation during percutaneous transluminal coronary angioplasty (“PTCA”), which is limited by processes that lead to re-occlusion within 3-6 months. PTCA has been one of the primary treatment modalities for revascularization of arterial stenoses. However, two aspects of PTCA have motivated cardiologists to seek alternative methods of treating the coronary stenosis: (1) acute ischemic complications related to vessel injury and the PTCA procedure itself, and (2) the occurrence of late restenosis, or reclosure of the treated site.
The occurrence of restenosis, or reclosure of the dilated vessel within 3-6 months of treatment, is the primary problem arising from the PTCA treatment and appears to be related to vascular injury. Damage to the vessel wall can lead to the release of thrombogenic, chemotactic, and growth factors. Endothelial denudation promotes platelet aggregation, thrombus formation, and activation of macrophages, lymphocytes, and smooth muscle cells. Activated platelets proceed to release additional mitogens including platelet derived growth factor (“PDGF”), fibroblast growth factor (“FGF”), and epidermal growth factor (“EGF”). Another contributing factor to loss of luminal diameter is the passive process of elastic recoil. The elastic nature of the vasculature promotes return to its original dimensions and can account for a significant loss of initial diameter gain. The excessive reparative response, compounded by elastic recoil, can become occlusive in itself propagating symptomatic recurrence including myocardial ischemia and angina. Alterations in local rheology such as turbulence and elevated shear stresses have also been associated with the restenosis process.
A significant decrease in numbers and rates of re-occlusion has been obtained by use of a mechanical cylindrically-shaped device, a stent, which maintains the expanded lumen against recoil and remodeling. Stents, which are typically made of a biocompatible metal, become incorporated within the vascular wall upon re-growth of the endothelium and are not removable. This feature can compromise re-treatment or treatment of distal portions of the stented vessel. Metallic stents can initiate a thrombogenic and immunogenic response, such as a foreign body response with inflammation. Moreover, metal stents have limited flexibility, making them difficult to deploy in smaller vessels. Because metal stents are permanent, their continued presence may interfere with future interventions and may lead to corrosion, perforation, and potential aneurysm. On an individual basis, the various metals being used may cause an allergic reaction.
Second generation stents have been developed in an attempt to address the problems listed above. Temporary metallic stents address the issue of permanence, but excessive trauma is associated with the retrieval process. Stent coatings, such as genetically engineered endothelial cells or various polymers have been employed in an attempt to reduce thrombogenicity. Polymers such as nylon, silicone, polyurethane, and fibrin have been tested with mixed results. Though data suggest some reduction in thrombus formation, other problems, including donor infection, optimization of formulation and delivery, and immunological response remain to be addressed. Stents comprised entirely of polmeric material offer an alternative to metallic stents. However, deployment techniques requiring heat, such as that required for polycaprolactone, can cause denaturation of adjacent tissues, and acidic breakdown products of biodegradable polymers can cause a significant inflammatory response. An additional consideration with biodegradable stents is the potential for atrophy of the musculoelastic elements in the arterial wall while the stent is in place, which may lead to aneurismal dilatation after the stent has been degraded. Finally, the polymer stents are intrinsically weaker than their metallic counterparts and additional bulk may be required to achieve adequate hoop strength.
Drugs capable of inhibiting thrombus formation and/or neointimal proliferation can be utilized, but systemic delivery of several appropriate and promising pharmaceutical agents has failed to demonstate clinical significance in reducing restenosis. This could result from a failure to achieve adequate local doses because of the toxic effect of high systemic delivery. Local delivery results in high local concentrations (up to ten times systemic concentrations) while avoiding toxicity. Polymeric stents or stent coatings can be used to incorporate or bind drugs with ensuing controlled, sustained, local drug delivery at the site of vascular injury.
Pharmaceutical coated stents are presently in the market and are being increasingly used. By attaching antithrombotic or antiproliferative pharmaceutical agents to the stent surface, reductions in restentosis rates have been reported. However, the mode of drug attachment can alter the biological activity of the compound, possibly due to masking of active sites or undesirable conformational changes. Furthermore, stents generally cover less than 10% of targeted vessel wall segments, resulting in nonuniform delivery to the arterial wall. Recent reports suggest an unfavorably high rate of allergic reactions and occlusive thrombotic responses to the coated stents.
What is needed, therefore, is a method for stabilizing the dilated vascular wall without the introduction of a foreign body, and also for maintaining the diameter of an artery expanded through balloon dilation in order to restore and maintain blood flow. What is also needed is a method for providing targeted, local drug delivery to the site of arterial expansion. Ideally, such a method should minimize the risks of restenosis and immune response. Such a method would also be useful for the local delivery of drugs, skin care materials, sunscreens, and cosmetics to the skin and to other anatomical, physical, surgical, and medical sites.